THIS is the tearful moment stunned Sex And The City star Cynthia Nixon discovers that her great-great-great-grandmother was an axe murderer.

The Emmy-winning actress was hoping for the sort of juicy gossip her on-screen character Miranda Hobbes would have devoured with relish when she decided to trace her real-life family tree.

Yet historians unearthed the shocking truth that her relative was thrown in jail for killing her husband.

Cynthia, 48, was confronted with the revelation in an episode of the US versiion of the hit TV series Who Do You Think You Are? which tracks celebrities’ ancestry and is due to air in the UK later this year.

However, after digging beyond local newspaper reports on the grisly murder in 1843, she reflected: “This poor woman endured so much tumult, turmoil and horror in her life that I am left with enormous admiration at the way she survived it all.”

The accounts of Martha Curnutt’s fatal attack on her violent and abusive husband Noah Casto were discovered by ancestry.com family historian ­Jennifer Utley in archive issues of the now-defunct Jefferson Inquirer in Missouri.

One said: “Casto had been in the habit of treating his wife in a manner too brutal and too shocking to think of. On the morning of the day mentioned, he told his wife to get up and get breakfast for herself and her two children, and then to commence saying her prayers, for she should die, he swore, before sunset.

“She got up and made a fire and returned to the room where her unnatural husband slept. He was lying on his back in a sound sleep. She took the axe with which she had been chopping wood and, with one blow, sunk it deep into his head, just through the eyes.”

Cynthia had an emotional time looking back at her family past [GETTY]

This poor woman endured so much tumult, turmoil and horror in her life

Cynthia Nixon

At her trial, Curnutt was spared the death penalty in recognition of the years of dreadful abuse by her husband, convicted of manslaughter and sentenced to five years in Missouri State Penitentiary, Jefferson City.

There her pitiful story took an even more bizarre twist when she gave birth to a daughter, Sarah, after almost a year in captivity as the sole female offender in the grim jail.

For a week after the birth, Curnutt and her infant were given barely enough food to survive and she was banned from having a stove to warm her cell like the male ­inmates.

With a gasp of realisation, Cynthia said: “It was as if they didn’t want the baby to survive because her birth could have led to a scandal.”

Her ­paternal relative somehow managed to keep both herself and her unclothed daughter alive, however, and their plight reached the ears of local and then national politicians who campaigned for her to be pardoned two years into her sentence.

The case became a turning point in America’s penal system and eventually led to women-only prisons for female offenders who until then had suffered the indignity of long-term incarceration in men’s jails.

As she stood with a bunch of wild flowers by Curnutt’s grave in Avery Cemetery in Leasburg, Missouri, Cynthia marvelled that her great-great-great-grandmother managed to live until the age of 75.

She said: “Martha’s strength was so towering. I admire her so much because she must have wanted to give up so many times but she didn’t and just kept on going.”